Revenue and Related Contract Costs and Contract Liabilities - Balance Sheet Reclassifications made to Separately Present Contract Costs and Contract Liabilities in Connection with Adoption of Topic 606 (Parenthetical) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Disaggregation Of Revenue [Line Items]
Reclassification of customer deposits to contract liabilities	$ 58,260	$ 31,981	[1]
Accounting Standards Update 2014-09
Disaggregation Of Revenue [Line Items]
Reduction in total current assets		700
Accounting Standards Update 2014-09 | Reclassification of Customer Deposits to Contract Liabilities
Disaggregation Of Revenue [Line Items]
Reclassification of customer deposits to contract liabilities		$ 33,400
Accounting Standards Update 2014-09 | Core Services
Disaggregation Of Revenue [Line Items]
Deferred costs included in other investments and assets	$ 4,400

[1] In connection with the adoption of Topic 606, we elected to more prominently present contract liabilities on the Consolidated Balance Sheets. Consequently, customer deposits of $33.4 million as of December 31, 2017, have been reclassified to “Contract liabilities” and to other certain current liabilities to conform to the current period presentation.